Celestion Neodymium 5" for bargain price?

[Phil_S]

So, what would you think of a 1x5, 2x5 or maybe a 4x5? Tempting just try it at this price. http://www.parts-express.com/pe/showdet ... er=299-416

PRODUCT SPECIFICATIONS
Power Handling (RMS) 25 Watts
Power Handling (max) 50 Watts
Impedance 8 ohms
Frequency Response 104 to 9,000 Hz
Sensitivity 89.2 dB 1W/1m
Voice Coil Diameter 1"

THIELE-SMALL PARAMETERS
Resonant Frequency (Fs) 104 Hz
DC Resistance (Re) 6.63 ohms
Voice Coil Inductance (Le) 0.26 mH
Mechanical Q (Qms) 2.49
Electromagnetic Q (Qes) 0.57
Total Q (Qts) 0.46
Compliance Equivalent Volume (Vas) 0.15 ft.³
Maximum Linear Excursion (Xmax) 1.13 mm

Oh boy, posted too soon. I found this bargain in a real guitar speaker: http://www.parts-express.com/pe/showdet ... er=299-464

[Blindog]

Hey Phil, did you end up getting the 12"? I saw that in my inbox from Parts Express and was very tempted..

[Phil_S]

I'm in the mode of resisting temptation at the moment. Sometimes you just have to let a bargain pass you by, but those little speakers are so cheap, I got to wondering about a 2x5 cab. I'd probably spend more to build the box than for the speakers, LOL.

[Geeze]

Where's the fun in resisting temptation? A lightweight and small cab that sounds good is certainly alluring. I am concerned about the 'buyout' comments from the parts place. It is my experience that only new things building a market or items that don't sell well go on 'on sale'.

[Phil_S]

You convinced me. I bought 2 of them....under $30 with postage. How can I go wrong? And if I do, so what?

This brings me to the question, what is the right size cab?

The speaker OD = ~6". I figure it needs a baffle 15" x 8" or maybe I can shave a little off the edges. Logic....2x 6" for the speakers + 1" bottom, top, and between, makes 15". Across, 6" + 1" on each side. This sets the size of the box except for depth.

I suppose I don't have to center the speakers, reducing length and adding width. I could make it diagonal and square. I don't see what that gets me. Is there something significant to making the box square...that would be 10.6 x 10.6 x 3.4, see below for depth.

The spec sheet says 0.11 cu ft for one speaker in a sealed (closed back?) box. I don't know much about speaker cabs. I suppose I should just double that? If so, that makes inside depth ~3.25". This seems shallow, but like I said, I don't know much. I'll have to see what the physical depth of the speaker actually is when I get it, as that isn't published.

There will be some frame braces to attach the baffle and the rear panel. These remove interior volume. I get to go a little deeper to compensate?

Maybe I need to go with "vented"? Does that mean open back? Spec says vented volume 0.25 cu ft. (.5 cu ft for two)?

Am I on the right track? Thanks for comments.

[Cantplay]

Vented implies ported box. Similar to the effect of blowing over a bottle.

The port can be round (PVC is popular) or rectangular. The length of the port determines its tuning. If port cross section is too small, the velocity will create port noise. I doubt that 2 5's can move enough air for that though.

There are also tapered horn type ports.

http://www.linearteam.dk/default.aspx?pageid=WinISD

WinISD is one of many free box calculator programs.

John

[Phil_S]

Thanks for the link, John. Like most of what I've been finding, these programs want to solve the problem from scratch -- at least that what it looks like to me.

There are some reviews on the partsexpress website and it seems I'll be better off with a ported cab if I want the bass frequencies. I'll take my chances on that being the right choice. That person says to double the cab size (2x .25 cu ft.) and the number of ports. He says the port for 89Hz is 1.5" ID and 1.5" long -- two little pieces of PVC from Home Depot, drill a couple of holes in the baffle and fix them with some goop?

Assuming I already know the cab size is 0.5 cu ft (provided by PE), I'm simply trying to understand if the aspect ratio of the baffle matters much or what. As I see it, the baffle size is the determining factor in the cab dimensions.

For 0.5 cu ft, assuming (for interior):
the speaker is 6"
there needs to be 1" between speakers
there needs to be 1" between the speaker and the edge of the baffle
then the baffle needs to be 15" long no matter what, and
any of the following sizes will work:
15 x 15 x 3.84
15 x 9.75 x 5.9
15 x 8 x 7.2
15 x 11 x 5.24

If it the choice doesn't matter, I'll go with 15 x 8 or 15 x 9.75 as the most compact and also fitting well with standard dimensional lumber. The widest standard dimensional lumber (12") is 11.25" and loses .75" front and back for the baffle and rear panels = 9.75" of interior.

Do I need to allow for (add to interior volume) the displacement of the braces for the baffle and rear panel, and for the actual displacement of the physical size of the speaker?

I'm new to this. Does any of it matter all that much?

Thanks for any advice.

[Cantplay]

http://www.mobileinformationlabs.com/Ho ... th%201.htm

Here is port calculator.

With PVC its easy to cut a few different lengths and experiment. Longer is lower.

John

[TUBEDUDE]

How about a 4 5" semi open back cab?
With the 16 ohm version, the speakers are half price.
Mini Bassman anyone?

[Phil_S]

LOL, this is a sleeper you're waking up! I bought 2 of these a while back but need to wait for the warm weather to do the cabinet work. I don't remember what Ohms mine are.

Checking PE, I see the 4r speakers for $10 and 8r speaker for $15 if you buy 12 of them or $19 for one. I don't see a 16r, but could have missed it.

In any case, you can use 4x 4r for 16r or 4r. When I build that 2x5" I'll post something about my impressions. It will probably be another couple of months yet. I have high hopes. If it isn't what I hope for, well, then I haven't lost much.

[TUBEDUDE]

Sorry Phil, brain fart, I meant four ohm.

[LeeMo]

When I was doing woofer boxes for car audio back in the day, I used a few tricks of the trade to tune a port to a cabinet. I used the same woofers over and over. I used a set range of box volumes. I used a graph (based on Thielle-Small math ) that was provided by the manufacturer which when you lined everything up would give you a close guess. At this time I would build the box and cut the port per the graph. Then I would hook it to an oscillator and do a sweep through the frequency that I wanted. When you hit the resonant peak that the port was tuned to , the woofer looks like it stops moving and the volume goes up quite a bit. I would put a small piece of masking tape on the cone to make it easier to see when it crossed the peak.
I don't know if this helps in guitar cabs. I just thought that I would share.

LeeMo

[Cantplay]

So, what frequency would you want to tune a guitar cab to?

What is the resonant frequently of a 4x12 slant cab?

John

[LeeMo]

I think that I recall a Celestion 12 " guitar speaker having a resonant peak at 70 hz. The low E is around 82 hz. Hendrix liked to use a bass cab with 55hz cones. Those 5 inch speakers have a resonance of 104 hz. ( in free air , no cab) .
I am by no means an expert nor an engineer. However I do know that below the tuned freq of a ported cab there is very little energy. The curve drops like a rock. Also, your ear doesn't need to hear the lows because it will hear the next octave up and fool itself into thinking the lower octave is there.
Wild azz guess ... tune it to 110hz . Slightly above the cones rez and an octave above Jimi's cone of choice. Your mileage may vary so don't hold me accountable, please.
That being said , you'll probably like it better sealed anyway, so make a port "cover" while you have the saw out.

Good Luck! LeeMo

[Phil_S]

Update time.

I built a closed back .5 cu ft box, inside dimensions about 19.5" x 9.75" x 5.7". I attempted two ports on the baffle with 1.5" pipe. This stuff isn't exactly 1.5" ID, but I adjusted accordingly. The calculator for 110Hz said ports should be .64" long. I got in trouble with the ports.

Without the gory carpentry mishaps, lets' just say I had trouble cutting good holes for the pipes. They weren't circle round or the right size, but I figured I could compensate with some goop of some sort.

Worse, I finally came to the conclusion that no matter how hard I tried, I couldn't cut the plastic pile so it was a) the correct length and b) plumb. (That's why they call it plumbing!) I chose to ignore the details and got a couple of pretty good cuts, which I glued into the baffle and sanded down to what I thought was the right length.

There was no hope of port covers. I need a good and properly sized hole saw.

Speakers mounted to the baffle reasonable well.

They have an acceptable range. Not muddy at the bottom (actually some decent low end) and OK at the top, too.

Here's the problem...buzz....buzzzzzzzzzzzzzzzzzzzzzzzzzzz. I think it's the ports. It is highly unlikely they are tuned to the same frequency and unlikely either is at 110Hz. I am unsure what path to take here.

Plug the port holes and just go with sealed? Easy enough to test this; yank the pipes and cover the holes.

Cut a new baffle and omit the pipe. After dealing with the problem, I see that I can cut two holes 1.5". The calculator says 1.5" x .48" is 110Hz. Still this won't be perfect because I don't really have a way of determining the exact interior volume of the box. I'd need to take it to a lab and fill it with water, then measure the water! The 12mm plywood, if perfect is .472" so that's not precise either.

I'm unsure about how precision relates to the ports.

Pics will be along later. I emailed from the phone and they take a while to arrive at the computer. I don't like to post using the phone -- too cumbersome.

Thoughts? Thanks.